236 GERM-CELL CYCLE IN ANIMALS 



an insect has a similar occurrence been noted, namely, 

 in Polyphemus, where, according to Kiihn (1911, 

 1913), the keimbahn-determinants consist of the 

 remains of one or more nurse cells (Fig. 50) . In the 

 DAPHNID^E (Weismann and Ischikawa, 1889) the 

 "Paracopulationszelle" arises from material cast out 

 by the germinal vesicle ; in JEquora (Haecker, 1892) 

 the "Metanucleolus" is likewise derived from the 

 germinal vesicle; in Ascaris (Boveri, 1892) chroma- 

 tin-diminution occurs during the two- to four-cell 

 stage; in Cyclops (Haecker, 1897, 1903) and other 

 copepods (Amma, 1911) the "Aussenkornchen" or 

 "Ectosomen" become visible soon after fertiliza- 

 tion (Diaptomus), but usually not until the pro- 

 nuclei fuse (other species) ; in Sagitta the "be- 

 sondere Korper" (Elpatiewsky, 1909, 1910) or 

 "Keimbahnchromidien" (Buchner, 1910) appear to 

 arise de novo after fertilization, although if Buchner's 

 contention that they are the remains of the accessory 

 fertilization cells is correct, they should be classed 

 with the " Nahrzellenkern " described by Kiihn 

 (1911, 1913) in Polyphemus. 



It is thus evident that the keimbahn-determinants 

 become visible, wherever they have been described, 

 either just before or just after the eggs are fertilized, 

 or, in parthenogenetic forms, shortly before matura- 

 tion and cleavage are inaugurated. 



The localization of the keimbahn-determinants at 

 the time of their appearance seems to be predeter- 

 mined. In insects the posterior end of the egg is 

 invariably the place where these bodies occur. In 



